The present invention relates generally to an organic EL (electroluminescent) device using an organic compound, and more specifically to an organic EL device less susceptible to light emission variations.
In recent years, organic EL devices have been under intensive investigation. One such device is basically built up of a thin film form of hole transporting material such as triphenyldiamine (TPD) deposited by evaporation on a hole injecting electrode, a light emitting layer of fluorescent material such as an aluminum quinolinol complex (Alq.sup.3) laminated thereon, and a metal (electron injecting) electrode of a metal having a low work function such as Mg and formed on the light emitting layer. This organic EL device now attracts attentions because a very high luminance ranging from several hundreds to tens of thousands cd/m.sup.2 can be achieved with a voltage of approximately 10 V.
As mentioned above, an organic EL device is basically made up of a substrate and an organic EL structure provided thereon, said organic EL structure comprising an electron injecting electrode, an organic layer or layers, a hole injecting electrode, etc. Usually, such an organic EL device is designed to take out the emitted light from a substrate side thereof.
When such organic EL devices are mass produced, there are often light emission luminance variations from device to device. For instance, a 20 nm variation in the thickness of the organic layer causes an approximately 20% fluctuation in light emission luminance. Such light emission luminance variations make it impossible to obtain desired results as designed, and to avoid them it is required to use additional equipment for luminance control, make the dimming range of a driving device or dimmer wider than needed, and regulate an end product made up of an organic EL device. These in turn incur increases in the cost of the product itself and labor incidental to the device such as preparation operations, and a drop of production efficiency.
If, in this case, the thickness of the organic layers is kept uniform, the light emission variations may then be controlled. However, it is very difficult, and unpractical, to make uniform the overall thickness of a multilayer structure comprising a plurality of different organic layers such as an electron injecting layer, an electron injecting and transporting layer, an electron transporting layer, a light emitting layer, a hole transporting layer, a hole injecting layer, and a hole injecting and transporting layer.